Compared to virtually any commercial segment, mil-aero testing does not traditionally deal with high-volume requirements over a relatively short period of time. Consider the case where a mil-aero company successfully breaks into the business of building transmit-receive (T-R) modules for phased-array radars. When this happens, the company in question typically moves from building one or a few units-per-radar to building hundreds or even thousands of units-per-radar, depending upon the radar application. Imagine being the test engineer working with a team of mixed-signal microwave component engineers who have spent the last few years designing and prototyping T-R modules. After multiple proposals, uncounted number of meetings, numerous design changes and the accumulation of literally thousands of hours of test data on a few prototypes, the engineering team has won the business of building several tens to hundreds of radars — each requiring at least two orders of magnitude more modules than the total number of prototypes built to date. In fact, the first manufacturing contract (block or tranche) may very well take about the same time to complete as the entire development period. And don't forget about the added requirement of needing to build and test extremely well-matched and high-performance T-R modules to the tune of a thousand times the number built during the engineering development and proposal stage.

The first production test plans are drawn and an analysis is made to correctly size and select the type of test equipment and number of stations needed to meet the production requirements. In support of the analysis, test time benchmarks are derived based upon the engineering test experience with prototypes. At the end of this process, the findings indicate that each module will require about four hours of test time, if the same approach that has been used during the engineering development phase is also applied to production. Considering the quantity of modules to be tested and the length of the contract, what are the financial and schedule impacts that these findings could have and what can be done to find a realistic, yet profitable solution?

Before answering the question above, let's find out more about the DUT. A T-R module is basically a miniature transmitter-receiver (transceiver) that needs to amplify and transmit phase- and amplitude-controlled wideband pulsed signals as well as to receive them. The T-R function requires fast switching and high isolation. All stages, especially the input/output ports, have to be well matched over the entire frequency band of operation. The T-R circuitry needs to be as efficient as possible (especially on the transmitter side) to reduce the power requirement as well as to generate as little heat as possible within the smallest possible form factor. This is important, because a certain number of modules will have to fit in a relatively small space. Heat and reliability (besides continuous and consistent performance) become a primary concern. Other parameters, such as harmonics, compression point/output dynamic range, third-order intercept (TOI), receiver noise figure (for best sensitivity), and duty cycle are also important.

Consequently, to ensure the quality and compliance of the DUT, all the parameters mentioned need to be carefully measured, optimized and validated during development, and quickly verified during production. Additionally, since these modules are frequency agile, can be electronically steered through a programmable phase shifter, and have variable output/input power, all the characteristic parameters need to be verified under a large variety of conditions and states. All of this leads to a measurement space defined as the number of measurement points in a multidimensional measurement volume that requires high-speed and high-measurement accuracy to achieve low uncertainty and allow testing to be efficiently and economically conducted. The test environment also has to be extremely stable in order for all measurements to exhibit good correlation, for the same module and among all modules, since the quality of an array will depend equally on the individual quality of each T-R module.

When testing in an engineering mode, not only do all parameters and characteristics of the T-R module prototypes need to be tested extensively but standard performance parameters are also methodically exceeded to be able to provide both performance (how much of an out of spec condition the module must endure) and manufacturing (how much of a variance due to components and production activities) margins. In this case, tests are bound to be extensively repeated, as the necessary modifications and rework are carried out, until the required performance and manufacturing parameters can be guaranteed. Consequently, during the engineering phase, test activities are almost as intense as they are in manufacturing, but they are more focused toward repeating tests on a few modules than performing tests once for each of many modules. During this phase, many companies start defining the test environment needed in production in order to avoid duplication of efforts and also to provide a seamless transition of the DUT test environment from engineering to production.

When testing in production, speed and accuracy are key. In order to be cost efficient, the production environment requires as few test stations as possible (with a minimum number of operators), with the highest throughput possible, while maintaining the highest possible yield. In this situation, two additional factors are of great importance:

1. A system-level calibration that is fully consistent and traceable to recognized standards (e.g., NIST). This ensures accuracy, low uncertainty, and consistent measurement results.

2. Consistency between the quality of the test environment in production and the test environment used during development. This contributes to high yield and highly correlated measurement results.

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